One of the best things to do is go to http://www.uspto.gov and do a free Trademark search. If something comes up as a match look to see if it has anything to do with the fitness industry. If not you may be able to use it but I recommend talking with a Patent and Trademark attorney first. I would also do extensive Google searches on the name(s) you wish to use to find out more about who may be using the name already. Look for an (R) or (TM) next to any of these names which will be a red flag. Be absolutely sure to do your homework on this first before buying domain names, putting up a website, having printed material done and so on. Good luck!